The present invention relates to golf balls and specifically to the construction of solid, non-wound, golf balls for regulation play. More particularly, the invention is directed to improved golf balls comprising multiple core assemblies which have a comparatively small, high density, polymeric center, or nucleus, component. The small, heavy center component in combination with the particular remaining core and cover components produces a golf ball having a smaller moment of inertia about its central axis. This results in a golf ball which exhibits enhanced spin while maintaining or improving additional golf ball characteristics such as durability, resiliency and compression.
Furthermore, the small, heavy weight, polymeric center component of the invention is preferably produced without the use of one or more peroxide crosslinking, or co-crosslinking agents comprising a metal salt of an unsaturated fatty or carboxylic acid. These crosslinking agents or coagents are the reaction product of an unsaturated carboxylic acid or acids and an oxide or carbonate of a metal such as zinc. Examples of such crosslinking agents, which again are preferably not incorporated into the present inventions, or if so, only to a minimal amount, include zinc diacrylate and zinc dimethacrylate. Accordingly, the polymeric centers of the golf balls of the present invention are generally free from peroxide crosslinking agents and exhibit high densities.
Additionally, in a more preferred aspect, the small, heavy center component of the invention is produced through the use of a blend of polybutadiene and polyisoprene rubbers. Powdered metal materials and other materials, including curing agents, may be incorporated therein to produce a high density, spherical center component that is commercially processible.
Moreover, in a particularly preferred aspect, the balls of the invention further utilize a multi-layer cover assembly. The improved multi-layer cover golf balls provide enhanced distance and durability properties over single layer cover golf balls while at the same time offering enhanced xe2x80x9cfeelxe2x80x9d and spin characteristics generally associated with soft balata and balata-like covers of the prior art.
Golf balls traditionally have been categorized in three different groups, namely, as one piece balls, multi-piece solid (two or more pieces) balls, and wound (three piece) balls. The one piece ball typically is formed from a solid mass of moldable material which has been cured to develop the necessary degree of hardness. It possesses no significant difference in composition between the interior and exterior of the ball. These balls do not have an enclosing cover. One piece balls are described, for example, in U.S. Pat. Nos. 3,313,545; 3,373,123; and, 3,384,612.
The wound ball is frequently referred to as a three piece ball since it is made with a vulcanized rubber thread wound under tension around a solid or semisolid center to form a wound core and thereafter enclosed in a single or multilayer covering of tough protective material. For many years the wound ball satisfied the standards of the U.S.G.A. and was desired by many skilled, low handicap golfers.
The three piece wound ball typically has a balata cover which is relatively soft and flexible. Upon impact, it compresses against the surface of the club producing high spin. Consequently, the soft and flexible balata covers along with the wound cores provide an experienced golfer with the ability to apply a spin to control the ball in flight in order to produce a draw or a fade or a backspin which causes the ball to xe2x80x9cbitexe2x80x9d or stop abruptly on contact with the green. Moreover, the balata cover produces a soft xe2x80x9cfeelxe2x80x9d to the low handicap player. Such playability properties of workability, feel, etc. are particularly important in short iron play with low swing speeds and are exploited significantly by high skilled players.
However, a three piece wound ball also has several disadvantages. For example, a wound ball is relatively difficult to manufacture due to the number of production steps required and the careful control which must be exercised in each stage of manufacture to achieve suitable roundness, velocity, rebound, xe2x80x9cclickxe2x80x9d, xe2x80x9cfeelxe2x80x9d, and the like.
Additionally, a soft wound (three piece) ball is not well suited for use by the less skilled and/or high handicap golfer who cannot intentionally control the spin of the ball. For example, the unintentional application of side spin by a less skilled golfer produces hooking or slicing. The side spin reduces the golfer""s control over the ball as well as reducing travel distance.
Similarly, despite all the benefits of balata, balata covered balls are easily cut and/or damaged if mishit. Consequently, golf balls produced with balata or balata containing cover compositions, can exhibit a relatively short life spans. As a result of this negative property, balata and its synthetic substitute, trans-polyisoprene, and resin blends, have been essentially replaced as the cover materials of choice by golf ball manufacturers by materials comprising ionomeric resins and other elastomers such as polyurethanes.
Conventional multi-piece solid golf balls, on the other hand, include a solid resilient core having single or multiple cover layers employing different types of material molded on the core. The one piece golf ball and the solid core for a multi-piece solid (nonwound) ball frequently are formed from a combination of materials such as polybutadiene and other rubbers cross linked with zinc diacrylate or zinc dimethacrylate, and containing fillers and curing agents which are molded under high pressure and temperature to provide a ball of suitable hardness and resilience. For multi-piece nonwound golf balls, the cover typically contains a substantial quantity of ionomeric resins that impart toughness and cut resistance to the covers.
Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of a unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. Metal ions, such as sodium or zinc, are used to neutralize some portion of the acidic group in the copolymer, resulting in a thermoplastic elastomer exhibiting enhanced properties, such as durability, for golf ball cover construction. However, some of the advantages gained in increased durability have been offset to some degree by decreases in playability. This is because, although the ionomeric resins are very durable, they also tend to be quite hard when utilized for golf ball cover construction and thus lack the degree of softness required to impart the spin necessary to control the ball in flight. Since most ionomeric resins are harder than balata, the ionomeric resin covers do not compress as much against the face of the club upon impact, thereby producing less spin. In addition, the harder and more durable ionic resins lack the xe2x80x9cfeelxe2x80x9d characteristic associated with the softer balata related covers.
As a result, while there are currently more than fifty (50) commercial grades of ionomers available, both from DuPont and Exxon, with a wide range of properties which vary according to the type and amount of metal ions, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups) and additive ingredients, such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the improved impact resistance and carrying distance properties produced by the xe2x80x9chardxe2x80x9d ionomeric resins, but also the playability (i.e. xe2x80x9cspinxe2x80x9d, xe2x80x9cfeelxe2x80x9d, etc.) characteristics previously associated with the xe2x80x9csoftxe2x80x9d balata covers, properties which are still desired by the more skilled golfer.
Moreover, a number of multi-piece solid balls have also been produced to address the various needs of the golfing populations. The different types of material used to formulate the core(s), cover(s), etc. of these balls dramatically alter the balls"" overall characteristics.
In this regard, various structures have been suggested using multilayer cores and single layer covers wherein the core layers have different physical characteristics. For example, U.S. Pat. Nos. 4,714,253; 4,863,167 and 5,184,828 relate to three piece solid golf balls having improved rebound characteristics in order to increase flight distance. The ""253 patent is directed towards differences in the hardness of the layers. The ""167 patent relates to a golf ball having a center portion and an outer layer having a high specific gravity. Preferably, the outer layer is harder than the center portion. The ""828 patent suggests that the maximum hardness must be located at the interface between the core and the mantle, and the hardness must then decrease both inwardly and outwardly.
Similarly, a number of patents for multi-piece solid balls suggest improving the spin and feel by manipulating the core construction. For example, U.S. Pat. No. 4,625,964 relates to a solid golf ball having a core diameter not more than 32 mm, and an outer layer having a specific gravity lower than that of the core. In U.S. Pat. No. 4,650,193, it is suggested that a curable core elastomer be treated with a cure altering agent to soften an outer layer of the core. U.S. Pat. No. 5,002,281 is directed towards a three piece solid golf ball which has an inner core having a gravity greater than 1.0, but less than or equal to that of the outer shell which must be less than 1.3. U.S. Pat. Nos. 4,848,707 and 5,072,944 disclose three-piece solid golf balls having center and outer layers of different hardness. Other examples of such dual layer cores can be found in, but are not limited to, the followings patents: U.S. Pat. Nos. 4,781,383; 4,858,924; 5,002,281; 5,048,838; 5,104,126; 5,273,286; 5,482,285 and 5,490,674. It is believed that all of these patents are directed to balls with single cover layers.
Multilayer covers containing one or more ionomeric resins have also been formulated in an attempt to produce a golf ball having the overall distance, playability and durability characteristics desired. This was addressed in U.S. Pat. No. 4,431,193, where a multilayered golf ball cover is described as having been produced by initially molding a first cover layer on a spherical core and then adding a second cover layer. The first or inner layer is comprised of a hard, high flexural modulus resinous material to provide a gain in coefficient of restitution while the outer layer is a comparatively soft, low flexural modulus resinous material to provide spin and control. The increase in the coefficient of restitution provides a ball which serves to attain or approach the maximum initial velocity limit of 255 feet per second, as provided by the United States Golf Association (U.S.G.A.) rules. The relatively soft, low flexural modulus outer layer provides for an advantageous xe2x80x9cfeelxe2x80x9d and playing characteristics of a balata covered golf ball.
In various attempts to produce a durable, high spin ionomeric golf ball, the golfing industry has also blended the hard ionomer resins with a number of softer ionomer resins. U.S. Pat. Nos. 4,884,814 and 5,120,791 are directed to cover compositions containing blends of hard and soft ionomeric resins. The hard copolymers typically are made from an olefin and an unsaturated carboxylic acid. The soft copolymers are generally made from an olefin, an unsaturated carboxylic acid and an acrylate ester. It has been found that golf ball covers formed from hard-soft ionomer blends tend to become scuffed more readily than covers made of hard ionomer alone.
Most professional golfers and good amateur golfers desire a golf ball that provides good distance when hit off a driver, control and stopping ability on full iron shots, and high spin for short xe2x80x9ctouch and feelxe2x80x9d shots. Many conventional two piece and thread wound performance golf balls have undesirable high spin rates on full shots. The excessive spin on full shots is a sacrifice made in order to achieve more spin on the shorter touch shots. Consequently, it would be desirable to produce a multi-piece golf ball that exhibited low spin on full iron and wood shots and high spin in the xe2x80x9ctouchxe2x80x9d and xe2x80x9cfeelxe2x80x9d shots which occur with the high lofted irons and wedges around the green.
In this regard, the multi-piece nonwound balls, while having an advantage with respect to cut resistance, typically have a cover that is sufficiently hard so as to provide low deformation upon impact and a small contact area between the ball and the club face. This provides a greater degree of xe2x80x9cslipperinessxe2x80x9d on the club face and, therefore, less control over the ball and greater difficulty in stopping the ball on the green when using short irons. At least some of these deficiencies are considered to result also from a large moment of inertia exhibited by the multi-piece balls. Thus, it would be useful to develop a ball with a controlled moment of inertia coupled with a soft cover layer in order to provide the desired backspin when using short irons, but at the same time without adversely impacting the desired flight and roll distance of the ball when using a driver.
A dual core, dual cover ball is described in U.S. Pat. No. 4,919,434. However, the patent emphasizes the hardness characteristics of all layers, particularly the requirement for a soft inner cover layer and a hard outer cover layer. With respect to the core, it requires that the layers should not differ in hardness by more than 10 percent and should be elastomeric materials having a specific deformation range under a constant load.
U.S. Pat. No. 5,104,126 attempts to concentrate the weight of the golf ball in the center core region by utilizing a metal ball as the core component. However, that patent teaches the use of a solid metal ball as the core component which provides substantially different properties than a polymeric core. Moreover, that patent also teaches the use of density reducing filler materials incorporated elsewhere in the golf ball. Although perhaps satisfactory in some respects, in other respects, it is undesirable to add density reducing fillers to offset the weight of the center core component. Additionally, it would be desirable to simply avoid the use of density reducing fillers if possible as they tend to lower the resilience of the golf ball.
Moreover, golf balls utilized in tournament or competitive play today are regulated for consistency purposes by the United States Golf Association (U.S.G.A.). In this regard, there are five (5) U.S.G.A. specifications which golf balls must meet under controlled conditions. These are size, weight, velocity, driver distance and symmetry.
Under the U.S.G.A. specifications, a golf ball can not weigh more than 1.62 ounces (with no lower limit) and must measure at least 1.68 inches in diameter (with no upper limit). However, as a result of the openness of the upper or lower parameters in size and weight, a variety of golf balls can be made. For example, golf balls are manufactured today by the Applicants which are slightly larger (i.e., approximately 1.72 inches in diameter) while meeting the weight, velocity, distance and symmetry specifications set by the U.S.G.A.
Additionally, according to the U.S.G.A., the initial velocity of the ball must not exceed 250 ft/sec. with a 2% maximum tolerance (i.e., 255 ft/sec.) when struck at a set club head speed on a U.S.G.A. machine. Furthermore, the overall distance of the ball must not exceed 280 yards with a 6% tolerance (296.8 yards) when hit with a U.S.G.A. specified driver at 160 ft/sec. (clubhead speed) at a 10 degree launch angle as tested by the U.S.G.A. Lastly, the ball must pass the U.S.G.A. administered symmetry test, i.e., fly consistency (in distance, trajectory and time of flight) regardless of how the ball is placed on the tee.
While the U.S.G.A. regulates five (5) specifications for the purposes of maintaining golf ball consistency, alternative characteristics (i.e., spin, feel, durability, distance, sound, visibility, etc.) of the ball are constantly being improved upon by golf ball manufacturers. This is accomplished by altering the type of materials utilized and/or improving construction of the balls. For example, the proper choice of the materials for the cover(s) and core(s) are important in achieving certain distance, durability and playability properties. Other important factors controlling golf ball performance include, but are not limited to, cover thickness and hardness, core stiffness (typically measured as compression), ball size and surface configuration.
Accordingly, a wide variety of golf balls have been designed and are available to suit an individual player""s game. In essence, different types of balls have been specifically designed or xe2x80x9ctailor madexe2x80x9d for high handicap versus low handicap golfers, men versus women, seniors versus juniors, etc. Moreover, improved golf balls are continually being produced by golf ball manufacturers with technological advancements in materials and manufacturing processes.
Two of the principal properties involved in a golf ball""s performance are resilience and compression. Resilience is generally defined as the ability of a strained body, by virtue of high yield strength and low elastic modulus, to recover its size and form following deformation. Simply stated, resilience is a measure of energy retained to the energy lost when the ball is impacted with the club.
In the field of golf ball production, resilience is determined by the coefficient of restitution (C.O.R.), the constant xe2x80x9cexe2x80x9d which is the ratio of the relative velocity of an elastic sphere after direct impact to that before impact. As a result, the coefficient of restitution (xe2x80x9cexe2x80x9d) can vary from 0 to 1, with 1 being equivalent to a perfectly or completely elastic collision and 0 being equivalent to a perfectly or completely inelastic collision.
Resilience (C.O.R.), along with additional factors such as club head speed, club head mass, angle of trajectory, ball size, density, composition and surface configuration (i.e., dimple pattern and area of coverage) as well as environmental conditions (i.e., temperature, moisture, atmospheric pressure, wind, etc.) generally determine the distance a golf ball will travel when hit. Along this line, the distance a golf ball will travel under controlled environmental conditions is a function of the speed and mass of the club and the size, density, composition and resilience (C.O.R.) of the ball and other factors. The velocity of the club, the mass of the club and the angle of the ball""s departure are essentially provided by the golfer upon striking. Since club head, club head mass, the angle of trajectory and environmental conditions are not determinants controllable by golf ball producers and the ball size and weight are set by the U.S.G.A., these are not factors of principal concern among golf ball manufacturers. The factors or determinants of interest with respect to improved distance are generally the coefficient of restitution (C.O.R.), spin and the surface configuration (dimple pattern, ratio of land area to dimple area, etc.) of the ball.
The coefficient of restitution (C.O.R.) in solid core balls (i.e., molded cores and covers) is a function of the composition of the molded core and of the cover. The molded core and/or cover may be comprised of one or more layers such as in multi-layered balls.
In balls containing a wound core (i.e., balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings. As in the solid core balls, center and cover of a wound core ball may also consist of one or more layers.
The coefficient of restitution of a golf ball can be analyzed by determining the ratio of the outgoing velocity to the incoming velocity. In the examples of this writing, the coefficient of restitution of a golf ball was measured by propelling a ball horizontally at a speed of 125+/xe2x88x921 feet per second (fps) against a generally vertical, hard, flat steel plate and measuring the ball""s incoming and outgoing velocity electronically. Speeds were measured with a pair of Oehler Mark 55 ballistic screens (available from Oehler Research Austin Tex.), which provide a timing pulse when an object passes through them. The screens are separated by 36xe2x80x3 and are located 25.25xe2x80x3 and 61.25xe2x80x3 from the rebound wall. The ball speed was measured by timing the pulses from screen 1 to screen 2 on the way into the rebound wall (as the average speed of the ball over 36xe2x80x3), and then the exit speed was timed from screen 2 to screen 1 over the same distance. The rebound wall was tilted 2 degrees from a vertical plane to allow the ball to rebound slightly downward in order to miss the edge of the cannon that fired it.
As indicated above, the incoming speed should be 125+/xe2x88x921 fps. Furthermore, the correlation between C.O.R. and forward or incoming speed has been studied and a correction has been made over the +/xe2x88x92 fps range so that the C.O.R. is reported as if the ball had an incoming speed of exactly 125.0 fps.
The coefficient of restitution must be carefully controlled in all commercial golf balls if the ball is to be within the specifications regulated by the U.S.G.A. As discussed to some degree above, the U.S.G.A. standards indicate that a xe2x80x9cregulationxe2x80x9d ball cannot have an initial velocity exceeding 255 feet per second in an atmosphere of 75xc2x0 F. when tested on a U.S.G.A. machine. Since the coefficient of restitution of a ball is related to the ball""s initial velocity, it is highly desirable to produce a ball having sufficiently high coefficient of restitution (C.O.R.) to closely approach the U.S.G.A. limit on initial velocity, while having an ample amount of softness (i.e., hardness) to produce the desired degree of playability (i.e., spin, etc.).
Furthermore, as mentioned above, the maximum distance a golf ball can travel (carry and roll) when tested on a U.S.G.A. driving machine set at a club head speed of 160 feet/second is 296.8 yards. While golf ball manufacturers design golf balls which closely approach this driver distance specification, there is no upper limit for how far an individual player can drive a ball. Thus, while golf ball manufacturers produced balls having certain resilience characteristics in order to approach the maximum distance parameter set by the U.S.G.A. under controlled conditions, the overall distance produced by a ball in actual play will vary depending on the specific abilities of the individual golfer.
The surface configuration of a ball is also an important variable in affecting a ball""s travel distance. The size and shape of the ball""s dimples, as well as the overall dimple pattern and ratio of land area to dimpled area are important with respect to the ball""s overall carrying distance. In this regard, the dimples provide the lift and decrease the drag for sustaining the ball""s initial velocity in flight as long as possible. This is done by displacing the air (i.e., displacing the air resistance produced by the ball from the front of the ball to the rear) in a uniform manner. Moreover, the shape, size, depth and pattern of the dimple affect the ability to sustain a ball""s initial velocity.
As indicated above, compression is another property involved in the overall performance of a golf ball. The compression of a ball will influence the sound or xe2x80x9cclickxe2x80x9d produced when the ball is properly hit. Similarly, compression can effect the xe2x80x9cfeelxe2x80x9d of the ball (i.e., hard or soft responsive feel), particularly in chipping and putting.
Moreover, while compression of itself has little bearing on the distance performance of a ball, compression can affect the playability of the ball on striking. The degree of compression of a ball against the club face and the softness of the cover strongly influences the resultant spin rate. Typically, a softer cover will produce a higher spin rate than a harder cover. Additionally, a harder core will produce a higher spin rate than a softer core. This is because at impact a hard core serves to compress the cover of the ball against the face of the club to a much greater degree than a soft core thereby resulting in more xe2x80x9cgrabxe2x80x9d of the ball on the clubface and subsequent higher spin rates. In effect the cover is squeezed between the relatively incompressible core and clubhead. When a softer core is used, the cover is under much less compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.
The term xe2x80x9ccompressionxe2x80x9d utilized in the golf ball trade generally defines the overall deflection that a golf ball undergoes when subjected to a compressive load. For example, PGA compression indicates the amount of change in golf ball""s shape upon striking.
The development of solid core technology in two-piece balls has allowed for much more precise control of compression in comparison to thread wound three-piece balls. This is because in the manufacture of solid core balls, the amount of deflection or deformation is precisely controlled by the chemical formula used in making the cores. This differs from wound three-piece balls wherein compression is controlled in part by the winding process of the elastic thread. Thus, two-piece and multilayer solid core balls exhibit much more consistent compression readings than balls having wound cores such as the thread wound three-piece balls.
Additionally, cover hardness and thickness are important in producing the distance, playability and durability properties of a golf ball. As mentioned above, cover hardness directly affects the resilience and thus distance characteristics of a ball. All things being equal, harder covers produce higher resilience. This is because soft materials detract from resilience by absorbing some of the impact energy as the material is compressed on striking.
However, soft covered balls are generally preferred by the more skilled golfer because he or she can impact high spin rates that give him or her better control or workability of the ball. Spin rate is an important golf ball characteristic for both the skilled and unskilled golfer. As mentioned, high spin rates allow for the more skilled golfer, such as PGA and LPGA professionals and low handicap players, to maximize control of the golf ball. This is particularly beneficial to the more skilled golfer when hitting an approach shot to a green. The ability to intentionally produce xe2x80x9cback spinxe2x80x9d, thereby stopping the ball quickly on the green, and/or xe2x80x9cside spinxe2x80x9d to draw or fade the ball, substantially improves the golfer""s control over the ball. Thus, the more skilled golfer generally prefers a golf ball exhibiting high spin rate properties.
In view in part of the above information, a number of one-piece, two-piece (a solid resilient center or core with a molded cover), three-piece wound (a liquid or solid center, elastomeric winding about the center, and a molded cover), and multi-layer solid or wound golf balls have been produced to address the various needs of golfers exhibiting different skill levels. The different types of materials utilized to formulate the core(s), cover(s), etc. of these balls dramatically alter the balls"" overall characteristics.
It would be useful to develop a golf ball exhibiting a high spin rate at low club head speeds when using short, high lofted irons. Such a ball would exhibit not only high spin but would also have a combination of softness and durability which is better than the softness-durability combination of a golf ball cover made from a hard-soft ionomer blend. Furthermore, it would be beneficial to produce a high spin golf ball that produces enhanced spin characteristics independent of its specific cover composition alone.
These and other objects and features of the invention will be apparent from the following summary and description of the invention, the drawings and from the claims.
Accordingly, it is a feature of the present invention to provide a multi-piece, nonwound, solid golf ball. The core is of a multilayer construction consisting of two or more polymeric components. The characteristics of the polymeric components of the core are such that the moment of inertia may be adjusted to enhance the backspin of the ball when using short irons.
An additional feature of the invention is to provide a ball having a multilayer polymeric core enclosed by a multi-layer cover. The ball has an appropriate moment of inertia that will permit extended flight distance of the ball and good roll when using a driver, coupled with a cover having sufficient softness that will permit deformation of the ball upon impact, thereby increasing the contact area between the ball and the club face without subjecting the cover to undesirable cutting or abrasion.
Another feature of the present invention is the provision for a golf ball of the type described that comprises both multilayer cores and cover(s) in such a manner as to incorporate the desirable features associated with various categories of balls traditionally employed.
A further feature of the present invention is the provision for a golf ball core structure with an inner or center polymeric core and an outer polymeric core layer, with the inner core having a specific gravity that differs from that of the outer core layer by more than 2.0, preferably more than 3.0, and most preferably more than 6.0, thereby giving the golf ball a moment of inertia differing from that of typical solid core balls.
Yet another feature is the provision for a multilayer core that is combined with a multilayer cover wherein the outer cover layer has a lower hardness value than the inner cover layer.
A still further feature of the invention is the provision for a golf ball having a soft outer cover layer with good scuff resistance and cut resistance coupled with relatively high spin rates at low club head speeds.
The present invention provides in an additional aspect, a solid, nonwound golf ball, and comprising a multi-core assembly that is concentrically positioned within the center of the golf ball, and a multi-layer cover assembly disposed about the multi-core assembly. The mass and position of both the multi-core assembly and the multi-layer cover assembly are such that the moment of inertia of the golf ball is less than 0.45 oz. in2, preferably less than 0.44 oz. in2, and more preferably, less than 0.43 oz. in2 for a 1.680xe2x80x3 golf ball.
In yet another aspect, the present invention provides a golf ball comprising a center core component which is concentrically disposed about a reference point located at the geometric center of the golf ball. The golf ball further comprises an outer core layer which generally surrounds and is disposed about the center core component. The golf ball further comprises a first inner cover layer disposed and positioned around the outer core layer, and a second outermost dimpled cover layer that is disposed about the first inner cover layer. Preferably, an ionomeric material is used in at least one of the cover layers. The configuration of the golf ball is such that it has a moment of inertia is preferably less than 0.43 oz. in2 for a 1.680xe2x80x3 golf ball.
In yet another aspect, the present invention provides a golf ball comprising a center polymeric core component having a specific gravity in the range of from about 1.2 to about 20, preferably about 2.0 to about 18.0, and a diameter in the range from about 5 mm to about 21 mm, preferably less than 10 mm. The golf ball further comprises an outer core polymeric layer disposed about the center core layer component, the outer core layer having a specific gravity in the range from about 0.9 to about 1.2, and an outer diameter in the range from about 30 mm to about 40 mm. The golf ball further includes an inner cover layer disposed about the core layer, and an outer cover layer disposed about the inner cover layer. The golf ball more preferably exhibits a moment of inertia of less than 0.43 oz. in2, and a coefficient of restitution of at least 0.760, preferably at least 0.780, and most preferably at least 0.800.
In a still further aspect, the present invention relates to a multiple core component, non-wound, golf ball having small, high density, spherical center which overcomes the above-referenced problems and others. In this regard, a smaller (i.e., a diameter of from about 5 mm. to about 21 mm) and heavier spherical center or center core layer is produced using a blend composed of a first polymer matrix material comprising a mix of polybutadiene and polyisoprene rubbers and metal particles, or other high specific gravity filler materials. The blend is preferably devoid of any metal carboxylate cross-linking or co-crosslinking agents generally present in solid core golf ball production.
In this respect, the high density center is encapsulated by one or more outer core layers and a cover assembly comprising one or more layers. The outer core layer(s) comprise a second polymer matrix material. The size and weight of the outer core layer(s) comprising a second polymeric matrix material and/or cover layers are adjusted in order to produce an overall golf ball which meets, or is less than, the 1.62 ounce maximum weight limitation specified by the U.S.G.A.
It has been found that the combination of the present invention produces a golf ball with a decreased moment of inertia and/or a lower radius of gyration. This results in the generation of higher spin without substantially affecting the resiliency of the ball. Additionally, the golf ball of the present invention exhibits a substantially similar or enhanced feel (i.e., softer compression) and overall durability.
In an additional aspect, the claimed subject matter of the present invention provides a golf ball comprising a dual polymeric core and a cover. The dual core has an inner, high density, spherical center core layer and at least one outer core layer. The high density, spherical center comprises a blend of high density powdered metal and/or other heavy weight filler materials and a first polymer matrix material selected from thermosets, thermoplastics, and combinations thereof. Preferably, the first polymer matrix material comprises a blend of about 90 to about 10 weight percent polybutadiene and of about 10 to about 90 weight percent polyisoprene. More preferably, the first polymer matrix material comprises of a blend of about 70 to about 30 weight percent polybutadiene and from about 30 to about 70 weight percent polyisoprene.
Moreover, in this aspect, the inner, high density, center core layer is preferably produced without the use of metal carboxylic crosslinking agents that are generally utilized in solid golf ball core production. These crosslinking agents are the reaction product of an unsaturated carboxylic acid or fatty acids and an oxide or carbonate of a metal such as zinc. Included are metal salts of unsaturated fatty acids, for example zinc, aluminum, and calcium salts of unsaturated fatty acids having 3 to 8 carbon atoms, such as acrylic acid and methacrylic acid.
The size and weight of the center of this aspect is configured in a manner to produce a low moment of inertia and a reduced rate of gyration. For example, the inner spherical center core layer has a specific gravity of greater than 1.2, preferably greater than 4.0, and most preferably greater than 7.0.
A lower density outer core layer is disposed about the high density spherical center core layer. The outer core layer comprises a second polymer matrix material selected from thermosets, thermoplastics, and combinations thereof. The second and first polymer matrix materials can be of the same or different compositions. A cover is then molded about the dual core.
In a still additional aspect, the present invention is directed to an improved dual core golf ball having a relatively small, high density spherical center or nucleus containing powdered tungsten (or other high density powdered metals) in a first elastomeric matrix, such as a blend of polybutadiene and polyisoprene. The powdered metal elastomeric matrix is peroxide, sulfur or radiation crosslinked. Preferably no zinc diacrylate (ZDA), zinc dimethyl acrylate (ZDMA) or other unsaturated carboxylic cross-linking agents are included in the inner spherical center.
One or more outer core layers are disposed about the high density center, followed by one or more cover layers. The outer core and/or cover layers are made lighter and/or thicker in order to produce an overall golf ball which conforms with the weight and size requirements of the U.S.G.A. This combination of weight and size displacement decreases the moment of inertia and/or allows the radius of gyration of the ball to move closer to the center.
The solid, non-wound, golf balls of the invention will have a moment of inertia of less than 0.45 oz.in2, preferably less than 0.44 oz.in2 for a standard size golf ball. More preferably the moment of inertia is less than 0.43 oz.in2 for a 1.680xe2x80x3 diameter golf ball. The moment of inertia for oversized or enlarged golf balls, such as balls 1.70-1.72 inches in diameter, is also reduced.
The moment of inertia (i.e., xe2x80x9cMOIxe2x80x9d) of a golf ball (also known as xe2x80x9crotational inertiaxe2x80x9d) is the sum of the products formed by multiplying the mass (or sometimes the area) of each element of a figure by the square of its distance from a specified line such as the center of a golf ball. This property is directly related to the xe2x80x9cradius of gyrationxe2x80x9d of a golf ball which is the square root of the ratio of the moment of inertia of a golf ball about a given axis to its mass. It has been found that the lower the moment of inertia (or the closer the radius of gyration is to the center of the ball) the higher the spin rate is of the ball with all other properties being held equally.
In all of the above aspects, the present invention is directed, in part, to decreasing the moment of inertia of a solid, non-wound, golf ball by varying the weight arrangement and composition of the core (preferably the inner spherical center core layer and the outer core layer). By varying the weight, size and density of the components of the golf ball, the moment of inertia of a golf ball can be decreased. Additionally, different types of matrix materials and/or crosslinking agents, or lack thereof, can be utilized in the core construction in order to produce an overall solid, non-wound, golf ball exhibiting enhanced spin and feel while maintaining resiliency and durability.
In one other further aspect, the claimed subject matter of the present application provides a multi-layered covered golf ball comprising a dual core and a multi-layer cover. Again, the dual core comprises an inner high density spherical center core layer and at least one outer core layer. The inner spherical center comprises a blend of high density powdered metal and/or other high density material and a first matrix material selected from about a fifty percent/fifty percent blend of polybutadiene and polyisoprene. The spherical center has a specific gravity of greater than 1.2, such as from about 2.0 to about 20.0, preferably about 4.0 to 18.0, and most preferably, about 7.6-7.8 for a 0.340xe2x80x3-0.344xe2x80x3 (8.6-8.75 mm) center.
At least one outer core layer of lower density is disposed about the inner spherical center. The outer core layer comprises a second matrix material selected from thermosets, thermoplastics, and combinations thereof.
The golf ball of this aspect also comprises a multi-layer cover having at least an inner cover layer and outer cover layer. The inner cover layer is disposed about the outer core layer. The outer cover layer is disposed about and generally surrounds the inner cover layer. One or more intermediate layers may also be included.
The golf balls of the present inventions having a high density elastomeric nucleus, are more durable and softer than solid metal nucleus balls while increasing resiliency. The diameter of the center, or nucleus, is dependent upon the specific gravity of the chosen heavy weight filler and the first matrix material so that the maximum U.S.G.A. golf ball weight is not exceeded. The diameter range of the inner center or nucleus is from about 0.200xe2x80x3 (about 5 mm) to a maximum of about 0.830xe2x80x3 (21 mm), more preferably from about 0.300xe2x80x3 (about 7.6 mm) to about 0.380xe2x80x3 (about 9.65 mm). The most preferred diameter is {fraction (11/32)}xe2x80x3, or 0.340xe2x80x3 to 0.344xe2x80x3.
The density of the most preferred 0.340xe2x80x3 to 0.344xe2x80x3 center is less than about 20 grams/cc, preferably less than 12 grams/cc and most preferably less than 8 grams/cc. The density is set so that it will not exceed the U.S.G.A. golf ball weight requirement. These and other objects and features of the invention will be apparent from the following description and from the claims.